Oxide semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides. The working principle involves the receptor function of the oxide grain surface and the transducer function of the grain boundary. The utility factor of the sensing body also plays a role in determining gas response. Sensor design concepts are determined by considering these three factors. The requirements include selecting a base oxide with high electron mobility and stability, selecting a foreign receptor to enhance surface reactions, and fabricating a highly porous, thin sensing body. Recent progress in sensor design based on these factors is described. Semiconductor gas sensors typically use porous sintered blocks of semiconducting oxides like SnO₂, WO₃, ZnO, and In₂O₃. Thick- and thin-film sensors have been investigated for miniaturization. The sensor changes electrical resistance upon exposure to a target gas. Response transients are observed, with gas response (Rₐ/R₉) and response/recovery rates being important characteristics. Gas response depends on operating temperature and gas concentration. Selectivity is defined by the ratio of response to different gases. Semiconductor gas sensors have been studied for practical applications like gas leak detection and environmental monitoring. Since the 1960s, efforts have been made to improve gas response, selectivity, stability, and practicality. Further innovations are needed to expand gas sensor applications. Many gases are hazardous, while others are useful for diagnosis. Most gases are present at low concentrations, requiring excellent sensing characteristics. Establishing sensor design principles based on fundamental understanding is essential. This article aims to describe the state of the art in sensor design to advance semiconductor gas sensors. The gas sensing process involves two key functions: recognition of the target gas through gas-solid interaction (receptor function) and transduction of surface phenomena into electrical resistance change (transducer function). The complex nature of porous, polycrystalline sensing bodies makes understanding these functions challenging. The receptor function is provided by oxide grain surface chemical properties, while the transducer function involves surface space charge layers. The utility factor relates to the porous structure of the sensing body. Key factors—receptor, transducer, and utility functions—can be significantly changed by altering base oxides, foreign materials, and high-order structures.Oxide semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides. The working principle involves the receptor function of the oxide grain surface and the transducer function of the grain boundary. The utility factor of the sensing body also plays a role in determining gas response. Sensor design concepts are determined by considering these three factors. The requirements include selecting a base oxide with high electron mobility and stability, selecting a foreign receptor to enhance surface reactions, and fabricating a highly porous, thin sensing body. Recent progress in sensor design based on these factors is described. Semiconductor gas sensors typically use porous sintered blocks of semiconducting oxides like SnO₂, WO₃, ZnO, and In₂O₃. Thick- and thin-film sensors have been investigated for miniaturization. The sensor changes electrical resistance upon exposure to a target gas. Response transients are observed, with gas response (Rₐ/R₉) and response/recovery rates being important characteristics. Gas response depends on operating temperature and gas concentration. Selectivity is defined by the ratio of response to different gases. Semiconductor gas sensors have been studied for practical applications like gas leak detection and environmental monitoring. Since the 1960s, efforts have been made to improve gas response, selectivity, stability, and practicality. Further innovations are needed to expand gas sensor applications. Many gases are hazardous, while others are useful for diagnosis. Most gases are present at low concentrations, requiring excellent sensing characteristics. Establishing sensor design principles based on fundamental understanding is essential. This article aims to describe the state of the art in sensor design to advance semiconductor gas sensors. The gas sensing process involves two key functions: recognition of the target gas through gas-solid interaction (receptor function) and transduction of surface phenomena into electrical resistance change (transducer function). The complex nature of porous, polycrystalline sensing bodies makes understanding these functions challenging. The receptor function is provided by oxide grain surface chemical properties, while the transducer function involves surface space charge layers. The utility factor relates to the porous structure of the sensing body. Key factors—receptor, transducer, and utility functions—can be significantly changed by altering base oxides, foreign materials, and high-order structures.